The stirling engine is a well known machine which utilizes the thermodynamic stirling cycle for converting thermal energy into mechanical or electrical energy. In a typical stirling engine, a working gas such as air, hydrogen or helium is alternately heated by a heat source and cooled by a heat sink. The expansion and compression of the working gas in response to the heating and cooling cycle is used to drive one or more pistons which in turn typically drive a shaft or drive gear system.
One well known type of stirling engine is the displacer-type stirling engine which is described with reference to FIGS. 1A-1D. Referring first to FIG. 1A, the displacer-type stirling engine 100 includes one power piston 102 and a displacer 104. A working gas 106 moves in a chamber 108 from one side of the displacer 104 to the other side of the displacer 104. Heating one side of the chamber 108 and cooling the other side of the chamber 108 causes repeated alternate expansion and contraction of the working gas 106 on alternate sides of the displacer 104 which in turn causes the displacer 104 to move alternately between the hot and the cold side of the chamber 108. The working piston 102 is tightly sealed in a secondary chamber 110 in communication with the displacer chamber 108 and is forced upward during a power stroke as the working gas 106 on the hot side of the chamber expands. The working piston 102 may be mechanically linked by a crank shaft, for example, to the displacer 104 which times and coordinates their relative movements. The mechanical linkage, not shown, causes the working piston 102 to compress the working gas 106 and provides a downward movement (FIG. 1B) to the displacer 104. Heat is extracted from the working gas 106 by a regenerator 112 which aids in the compression of working gas 106 on the cold side of the displacer and causes this gas to move around the displacer and re-fill the hot side of the chamber (FIG. 1C). The cool working gas is then heated by the hot side of the chamber (FIG. 1D) to drive the power piston 102 and move the displacer 104 downward. Energy is thereby extracted from the working gas in response to a temperature differential between the hot and cold sides of the chamber.
Various systems and methods have been known for extracting energy from the oceans and converting the oceans' thermal energy to other forms of useful energy. The field of ocean thermal energy conversion (OTEC) holds much promise as a renewable energy source when certain technical barriers are overcome. In order to extract energy from the oceans, an OTEC system must include portions that extend from the warm ocean surface to much colder waters in the ocean depths. Disadvantageously, displacer-type stirling engines have been heretofore found to be impractical for use in OTEC systems due to the large sized displacement chambers that would be required and the various mechanical linkages which must span large distances.